The present invention relates to a method for determining a maximum speed limit for a reversing vehicle combination. The method is especially suited for use with a reverse assistance function.
Professional drivers of heavy trucks with trailers often have to perform low speed manoeuvres with high precision when marshalling. This could for example be when loading or loading the vehicle, docking at loading bays, parking in tight spaces, coupling trailers or changing swap bodies. When marshalling with a long vehicle combinations, even an experienced driver must be concentrated, and it may well be both stressful and time consuming.
One way to relieve the pressure on the driver when marshalling is to provide the truck with a reverse assistance function. The reverse assistance function will assist the driver when reversing the vehicle combination, thereby allowing the driver to supervise the manoeuvre. The reverse assistance will reduce the time spent during marshalling, e.g. the time spent to dock a loading platform, which will increase the productivity of the vehicle and the precision of the docking operation. Further, it may also reduce accidents that could damage both the vehicle combination and surrounding objects since the driver can be fully concentrated on supervising the vehicle motion rather than planning and executing the reversing of the vehicle combination. Another advantage is that also inexperienced drivers will be able to perform difficult marshalling tasks.
Reverse assistance is becoming increasingly popular by passenger cars, where the control task of the reverse assistant function often uses separate controllers for the steering and for the speed. The driver of the vehicle may e.g. control the reverse speed of the vehicle and the control system of the vehicle controls the steering of the vehicle when parallel parking. The system comprises some sort of speed limit such that the driver can only move the vehicle at a very low speed regardless of how much the throttle is engaged.
For a reverse assistance system that is to be used with a heavy vehicle such as a truck, other features are desirable. With a heavy vehicle, parallel parking is not a primary purpose. Instead, reversing over longer distances, e.g. for docking to a loading platform, is a useful feature. Further, the reverse assistance system should also be adapted to handle a vehicle combination comprising a truck and a trailer.
Also for such a system, it is of advantage to limit the speed of the vehicle combination in order to increase the safety and comfort. It is thus room for an improved method adapted to determine a maximum speed limit for a reversing vehicle combination.
It is desirable to provide an improved method for determining a maximum speed limit for a reversing vehicle combination. It is also desirable to provide a method for determining a maximum speed profile for a reversing vehicle combination.
In a method for determining a maximum speed limit for a reversing vehicle combination comprising a towing vehicle and at least one towed trailer, the steps of determining a manoeuvre that is to be performed by the vehicle combination, simulating the complete manoeuvre in advance by using a control algorithm and a state space model, thereby obtaining the steering behaviour of the vehicle combination during the manoeuvre, and calculating the maximum speed limit for the vehicle combination during the manoeuvre by using at least one predefined limiting condition are comprised.
By this first embodiment of the method, the method can determine a maximum speed limit for a vehicle combination during an assisted reverse manoeuvre. The speed limit is calculated by using one or more limiting conditions for the vehicle and/or for the driver. The limiting conditions may comprise the maximum steering rate of the steering actuator of the towing vehicle, the maximum braking capacity of the vehicle combination and comfort limitations for the driver. The maximum steering rate of the steering actuator is one important factor due to the fact that, if the steering actuator is too slow for the actual vehicle speed, the vehicle will deviate from the predefined track. In such a case, the vehicle may not reach the predefined position or it may drive in to obstacles positioned outside of the planned path. It is thus of advantage to simulate the manoeuvre in advance, taking account to different limiting conditions that may occur during the manoeuvre. The steering rate of the steering actuator will affect the maximum speed more or less depending on the sharpness of the turns that is to be made during the path. During a sharp turn, or when the desired curvature changes rapidly, the actuator rate will limit the allowed speed for the vehicle in order to stay on the predefined track. When the vehicle travels along a more or less constant straight or curved path, the actuator rate will probably not limit the allowed speed.
The braking capacity of the vehicle combination can also affect the maximum allowed speed of the vehicle combination. This limitation will affect the comfort of the driver and/or the forces imposed on the load of the vehicle combination. Another limiting condition that will affect the comfort of the driver and/or the load is e.g. the lateral acceleration.
In a development of the method, the manoeuvre of the vehicle combination is divided into several sub-paths, where a maximum speed limit is determined for each sub-path. In this way, a maximum speed profile for the manoeuvre is obtained. The actual speed of the vehicle combination during reversing can in this case be adapted to the type of manoeuvre and to the specific conditions during the manoeuvre. At a sharp turn, the speed limit is relatively low and may e.g. depend on the steering actuator rate, and at a straight segment, the speed may be limited by an upper speed limit.
The oeuvre that is to be performed may be selected from a list of stored manoeuvre paths. Such manoeuvres may be e.g., docking to a loading ramp, picking up a swap body that was previously delivered, parking in a parking space or reversing a path just travelled. Due to the type of manoeuvre, the path may be divided into several different sub-paths. Each sub-path may be defined as a path segment in which the steering of the towing vehicle displays the same sign. In this way, each change of direction will define a new sub-path. A sub-path may also be defined by a predetermined time interval or a predefined travelled distance.